Mechanical power assist apparatus

ABSTRACT

A power assist for a hand-operated punching machine comprises an output bar mounted for reciprocating movement, and normally spring-biased to a predetermined quiescent position. A motordriven pulley continuously operates to reciprocate a catch mechanism along a straight line path parallel to the normal direction of extension of the output bar; and the output bar is in turn provided with a pivotally mounted catch which is normally spring biased to a position spaced from the path of movement of the power driven catch. A treadle mechanism is provided for selectively repositioning the pivotally-mounted catch so that it engages the power-driven catch when said power-driven catch next passes the location of said pivotally-mounted catch; and this engagement between catches causes the output bar assembly to be driven upwardly in a power stroke. Upon completion of a single power stroke, the catch automatically disengages, and the output bar returns to its quiescent position where it remains until the treadle is again depressed. Locking means are provided for assuring that the treadle cannot be reactuated during occurrence of the power stroke.

United States Patent 1 Liepings [54] MECHANICAL POWER ASSIST APPARATUS [76] I lnventor: Janis Liepings, 427 North Huron,

Pierre, S. Dak.

221 Filed: June30, 1971 21] App1.No.:/158,l90

. [52] U.S. Cl. ..83/573, 83/588, 83/628 [51] Int. ,Cl. ..B26d 5/10 [58] Field of Search ..83/573, 588, 628; 74/50, 55, 74/122,125,l48,160,155,5l2

[56] References Cited UNITED STATES PATENTS 10/1853 Davie et al ..83/573 X 262,082 8/1882 Miles ..83/573 X 276,979 5/1883 Pease ..83/573 X 1,650,411 11/1927 Yates ..83/573 Primary Examiner Frank T. Yost Att0mey-William D. Hall et a1.

[57] ABSTRACT A power assist for a hand-operated punching machine [451 Feb. 13, 1973 comprises an output bar mounted for reciprocating movement, and normally spring-biased to a predetermined quiescent position. A motor-driven pulley continuously operates to reciprocate a catch mechanism 'along a' straight line path parallel to the normal direction of extension of the output bar; and the output bar is in turn provided with a pivotally mounted catch which is normally spring biased to a position spaced from the path of movement of the power driven catch. A treadle mechanism is provided for selectively repositioning the pivotally-mounted catch so that it engages the power-driven catch when said power-driven catch next passes the location of said pivotally-mounted catch; and this between catches causes the output bar assembly to be driven upwardly in a power stroke. Upon completion of a single power stroke, the catch automatically disengages, and the output bar returns to its quiescent position where it remains until the treadle is again A depressed. Locking means are provided for assuring that the treadle cannot be reactuated during occurrence of the power stroke.

10 Claims, 10 Drawing Figure s engagement PATENTED FEB 13 I975 SHEET 2 OF 5 INVENTOR Janis Liepins ATTORNEY PATENTEBFEB 13 I975 3.715.948

SHEET 3 BF 5 FIG. 3.

FIG. 4.

- :1- INVENTOR- Janis Liepi s 5 ATTORNEY PATENTED FEB 1 3 I973 SHEET Q 0F 5 FIG. 6.

INVENTOR Janis Liepins ATTORNEY PATENTED FEB 1 3 I975 SHEET 5 [IF 5 INVENTOR Janis Liepins ATTORNEY MECHANICAL POWER ASSIST APPARATUS BACKGROUND OF THE INVENTION Various mechanisms have been suggested heretofore for effecting powered operation of a punching machine or the like. Some of these prior arrangements include mechanisms so arranged that, upon manual initiation of a powered operation, the machine is caused to go through a single powered cycle, whereafter it comes to rest and awaits manual initiation of a next cycle. References of this type include Langenberg US. Pat. Nos. 2,390,376, Yoder 2,301,236, Ryan 2,289,076, Wood 2,045,744, Sherman 1,918,059, Bataille 1,653,979, Furber 1,650,119, and Swanson 1,353,292.

The references identified above depict a variety of machine tools provided with a continuously operating power source which is intermittently and selectively applied to produce a single powered stroke in the machine, whereafter the machine comes to rest until it is manually released for a further operation, etc. The

.arrangements contemplated by these prior references operate on principles different from those which characterize the present invention, as will become more readily apparent from the detailed description of the invention which appears hereinafter. Moreover,

these prior arrangements take the form of complete machines designed from their inception to achieve powered operations; and the prior arrangements do not lend themselves to use as power assists on pre-existing hand-operated machines, operative to convert such hand-operated equipment to powered operation.

In essence, therefore, the present inventionis concerned with a completely new power drive arrangement adapted to be attached to a pre-existing hand operated machine (e.g. a punching machine, a cutting machine, or the like) and operative to substantially increase the output of the pre-existing machine by means of a mechanism which is rugged, reliable, safe and foolproof in operation, and capable of being used by untrained personnel.

SUMMARY OF THE INVENTION the thickness of the paper determines the maximum capacity of the General Binding Corp: machine), the realized output of the equipment with the power assist added is approximately 9,000 sheets per hours, a quantity which cannot even be approached when the machine is operated manually.

The power assist of the present invention comprises an elongated output bar mounted in generally vertical position, and adapted to be selectively driven in a reciprocating motion, to operate the punch element of the punching machine which, otherwise, would have to be operated manually. Spring means are provided to bias the output bar to a predetermined quiescent posipivotally attached to the output bar, but is normally so I positioned that it is spaced from the path of movement of the aforementioned power-driven first catch. Operator means, preferably a treadle, is provided to selective-.

ly move the second catch to a position overlying the path ofmovement of the first catch so as to permit the first catch, during it reciprocating motion, to engage the second catch and to thereby move the second catch and its attached output bar away from its quiescent position in a power stroke. Means are provided to dis- I engage the second catch from the first catch upon completion of the power stroke so that, upon depression of the machines treadle, a single powered punching operation is effected.

The apparatus is so arranged that, once the treadle is depressed by an operator, it is automatically locked in its depressed position to prevent initiation of a further punching operation until full completion of the punching operation then in progress. When the treadle is depressed, it operates to move a wedge-type block into contact with a roller forming a portion of the aforementioned second catch, so as to pivot the catch relative to the aforementioned output bar into the path of movement of the continually driven first catch. The power stroke is then initiated by the sequence already described. As the power stroke progresses, upward movement of the output bar actuates a tiltable lever mechanism forming a portion of the power assist, and said lever mechanism operates to push the aforementioned treadle-actuated wedge in a rearward direction so as to produce a space into which the aforementioned second catch can be moved at or near completion of the power stroke, thereby to assure disengagement between the catches after one stroke has been completed. Completion of the power stroke in turn initiates a further sequence of operations, wherein the depressed treadle bar is unlocked and returned to its undepressed state, and the lever mechanism and treadle-operated wedge-type block are reset in position preparatory to initiation of a next subsequent power stroke.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of a punching machine having the power assist of the present invention added thereto;

FIG. 2 is a diagrammatic side view of the present invention;

FIG. 3 is a view similar to FIG. 2, showing other details of the structure shown in FIG. 2',

FIG. 4 is a view similar to FIGS. 2 and 3 illustrating the operation of the present invention; and;

FIGS. 2A, 5, 6, 7, 8, and 9 are detail views of various portions of the structure shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I As illustrated in FIG. 1, a punching machine employing the power assist of the present invention may combe punched. The punching operation is accomplished by moving a punching element through the sheets of paper; these elements being in themselves conventional and commercially available. The punching element is operated by a power assist mechanism, generally designated 13, comprising a pulley 14 driven via a belt 15 from a motor and transmission mechanism 16. Pulley 14, as will become apparent subsequently, drives an eccentrically mounted first catch, and guide means are provided for causing the first catch to describe a continual reciprocating straight line motion during rotation of pulley 14. A treadle 17, normally held in an upward position by retracting springs 18 (the tension of which can be adjusted by an adjusting mechanism 19) can be selectively depressed by the foot of an operator to initiate a power stroke by causing engagement between the aforementioned first catch, and a second catch carried 1 by an output bar. When the treadle 17 is so depressed, it is locked in its depressed position until completion of the power stroke.

The details of the power assist, shown generally in FIG. 1, will become more readily apparent from a consideration of FIGS. 2 through 9, like numerals of which refer to like parts throughout. The power assist includes a base plate 20 having an upstanding main plate 21 fastened at its lower end to base plate 20, and fastened at its upper end to the underside of cabinet top 11. The aforementioned retracting spring adjusting mechanism l9'is fastened to the front side of plate 21, and pulley 14 is rotatably fastened to the rear side of said plate 21. Upper and lower brackets 22 extend rearwardly from plate 21, and support a pair of spaced vertically extending guide bars 23a and 23b (see FIG.

- which act as guides to convert the. rotary motion of pulley 14 into a reciprocating straight line motion of a first catch 24.

More particularly, catch 24, which has an. inclined wedge configuration, is mounted on a plate structure 25 dimensioned to fit between guide bars 23a and 23b; and a pair of spaced horizontally extending bearing bars 260 and 26b are affixed to the plate 25. A bearing wheel 27 is disposed between bearing bars 26a and 26b,

and wheel 27 is in turn attached to pulley 14, at a position spaced from its center, by an axle 27a. The lengths of bearing bars 26a and 26b are sufficient to accommodate the complete range of lateral displacement of bearing wheel 27 as pulley 14 rotates; and, as a result, bearing bars 26a, 26b, and catch 24 attached thereto, are moved up and down in a reciprocating motion between vertical guide bars 23a, 23b as the pulley 14 rotates. A pair of roliers 25a and 25b, mounted on axles which are in turn attached to members extending upwardly and downwardly from plate 25, roll on bars 23a, 23b to guide the catch 24, and its associated mounting assembly, in the aforementioned reciprocating motion.

This entire portion of the structure operates, accordingly, to cause catch 24 to be reciprocated continually in substantially straight line motion as pulley 14 is driven by the motor 16 connected thereto.

A vertically extending plate 28 is attached to bearing bars 23a,-23b to hold said bearing bars in spaced parallel relation. Pairs of brackets 29 and 30 extend reartheir forward side, with a pair of further plates 32a, 32b

(see FIGS. 5, 6 and 9) which overhang the edges of bars 30a, 30b, but which are spaced from one another to permit passage of a catch mechanism 34 connected to an output bar 33 (to be described). The output bar 33 (see FIG. 7) is located between vertical guide bar 30a, 30b, and between plates 31, 32a, 32b for vertical sliding motion.

Output bar 33, as best shown in FIG. 7, is of elongated configuration and is bifurcated at its lower end to provide a pair of legs 33a, 33b. A catch 34 (see especially FIG. 8) is located between legs 33a, 33b of output bar 33, and comprises a block which is pivoted at its lower end, on a pivot 35, to said legs. A nose 36 ex tends outwardly from block 34, toward catch 24, and is provided with an inclined upper surface as illustrated. The upper end of block 34 is bifurcated and a roller 37 is mounted between said bifurcations on an axle 38.

A flat leaf spring 39 is mounted on output bar 33 at a position above catch 34, 36 and includes a pair of tongues (see FIG. 7) which extend into resilient engagement with block 34 at opposite sides of roller 37. Leaf spring 39 urges catch 34, 36 rearwardly about its pivot 35, relative to output bar 33 so that, under quiescent operating conditions, nose 36 of the output bar catch is spaced from the path of travel of driven catch 24, i.e., spring 39 urges catch 34 to such a position that it does not normally engage driven catch 24.

Output bar 33 includes a forwardly projecting adjustable lug 40 which operates, in the fashion to be described, to control the positioning of a tiltable lever mechanism (FIG. 9) mounted around the output bar retaining assembly. The upper end of output bar 33 includes a direction differential bar 41 pivoted to the outgated retracting springs 46 attached thereto, with the lower end of said springs 46 being anchored by bolt 46a to a bracket 46b near the bottom of the power assist (see FIGS. 2 and 5).

Springs 46 hold output bar 33 in a lower quiescent position between guides 30a, 30b with nose 36 of the catch 34 being located between plates 32a, 32b of the guide bar retaining assembly. The rear plate 31 of the guide bar retaining assembly is provided with an aper ture 31a having an upwardly inclined beveled surface 31b, and in the quiescent position of the output bar 33, spring 39 forces catch 34 rearwardly so that it projects partially through opening 31a with its roller 37 bearing on inclined surface 31b. The purpose of this structure will become apparent subsequently.

Foot pedal 17 is attached to a treadle bar 17a which is pivoted at 17b in a bracket extending upwardly from base plate 20. The end of treadle bar 17a remote from foot pedal 17 is bifurcated as at (see FIG. 6); and a lower end, and supports a wedge block 51 at its upper end. Block 51 has an inclined wedge surface 51a which is disposed in facing relation to roller 37 of catch 34, but which is normally spaced from said roller (see FIG. 2). Block 51 further includes a pair of outstanding pins 52 which cooperate with a cam mechanism forming a portion of the tiltable lever mechanism, to be described.

Apressure plate assembly 53 is mounted on plate 31 rearwardly of wedge block 51 and operates, under quiescent conditions, to urge block 51 into engagement with plate 31, at a position slightly below and spaced from roller 37 Pressure assembly 53 comprises a housing which includes a back plate 53a and spaced sides 53b the forward ends of which extend inwardly to provide spaced shoulders supporting apressure plate 54. Plate 54 is urged in a forward direction by a spring 55 (see FIG. 2) which is mounted on a keyed shaft 56 supported in turnon a block 57 acting as a shaft guide. The arrangement is such that pressure plate 54 is resiliently urged in a forward direction to hold the treadleoperated wedge block 51 firmly between pressure plate 54 and plate 31 at a position slightly below roller 37 of catch 34.

A tiltable lever mechanism generally designated 60 (see FIG. 9) is provided to control the position of treadle-operated block 51 during a portion of the operating cycle. Lever mechanism 60 comprises a pair of lever arms 61 (only one of which is shown) which are pivoted at bearings 62 to the opposing side bars 30a,

30b respectively of the output bar retaining assembly. The upper ends of lever arms 6l'have brackets 63 attached thereto', and a roller 64 mounted on an axle 65 extends between lever arms 61, with roller 64 being positioned between plates 32a, 32b of the guide bar retaining assembly along the path of movement of lug 40. The purpose of this arrangement will be described subsequently.

The lower ends of lever arms 61 have a pair of brackets 66 attached thereto, and the rear edges of said brackets 66 are formed in'a cam configuration and bear respectively on pins 52 outstanding from treadle operated block 51. The lower edge of each bracket 66 is provided with a pair of spaced notches 67, 68 which form a portion of a detent mechanism defining two predetermined tilt positions for the lever arms 61. More particularly, a pair of blocks 69 are mounted on the opposing sides of the guide bar retaining assembly (see FIG. 6) and include a pair of outwardly protruding spring biased pins 70" positioned to seat in either notches 67 or notches 68 to hold the lever arms 61 in a selected one of two possible tilt positions relative to their bearings 62.

.A treadle locking assembly is mounted on base plate for holding foot pedal 17 and treadle bar 17a in a depressed position, once it has been depressed, until a given cycle of operation is completed. The locking assembly comprises a slidable bolt 70 having a finger portion 70a receiving a compression spring 71 which bears between a portion of bolt 70 and the retaining bracket 72, the arrangement being such that bolt 70 tends to be resiliently urged in a rearward position. Bolt 70 is provided with an inclinedsurface 70b which is in turn engaged by acomplementary inclined surface 74a formed at the lower end of a vertically extending block 74.

Vertical block 74 is mounted for slidable movement in a pair of brackets 75, 76; and a spring member 77, extending between a portion of block 74 and lower bracket 75, normally urges block 74 in an upward direction. As best illustrated in FIG. 7, the upper end of block 74 is positioned directly below one side of output bar 33, at the lower end of said output bar. As a result, when output bar 33 is in its lowermost or quiescent position, it holds vertical block 74 downwardly against the spring 77; and wedge surface 74a of vertical block 74 in turn holds bolt in a forward position against the urging of its spring 71. For this position of the various parts, an upstanding leg 70c extends into an aperture l7c in treadle bar 17a; and the treadlebar is not locked. If the parts are released, however, bolt 70 can move in a rearward direction so that its leg 70c underlies a portion of treadle bar 17a rearwardly of pivot 17b (see FIG. 4) to hold the portion of the treadle bar forwardly of said pivot 17b in its depressed position.

Considering now the operation of the structure described, let us first assume that foot'pedal 17 is in its undepressed or upward position, and that pulley 14 is being rotated by the motor drive attached thereto. In this quiescent operating condition, output bar 33 is held in its lowermost position by retracting springs 46; catch 34 connected to the output bar is held in its rearward position in opening 31a of plate 31 by the force applied thereto by leaf spring 39; wedge block 51 is being held in position below roller 37 of catch 34 by pressure plate 54; and treadle bar 17a is held in its elevated position by springs 18. The retracted position of output bar '33 holds vertical block 74 in its lowermost position against the force of spring 77', and inclined wedge surface 74a of said vertical block 74 in turn holds sliding bolt 70 in its forward position against the force of spring 71. The tiltable lever arms 61 have their lowermost ends in a forward position, and are held in this predetermined position by spring pressed pins 70 protruding into notches 67 in brackets 66. The positioning of the parts is, in short, the same as is shown in FIGS. 2 and 3; and power driven catch 24 moves continually up and down in a reciprocating motion without causing any movement of output bar 33.

Let us now assume that foot pedal 17 is depressed by the operator, causing treadle bar 17a to tilt about its pivot 17b to move rod 50 and attached wedge block 51 upwardly. This upward movement of wedge block 51 causes its inclined surface 51a to engage roller 37 of catch 34, pushing catch 34 in a forward direction against the restraint of spring 39. If, at the instant that the treadle is depressed, power driven catch 24 is above catch 34, the lower surface of catch 24 engages the upper surface of nose 3 6 in catch 34 when said catch.

24 next moves in a downward direction; and this causes the catch 24 merely to push catch 34 in'a slight rearward direction sufficient to permit catch 24 to pass the position of catch 34 as catch 24 moves downward, whereafter catch 34 moves back to the position described.

When catch 24 next moves in an upward direction, its upper surface engages the lower surface of nose 36 to pull catch 34 and its attached output bar 33 in an upward direction. During the initial portion of this upward movement, roller 37 engages inclined surface 31b in plate 31, causing the the catch 34 to be pulled forward to a somewhat greater extent than was produced by wedge block 51, thereby assuring a firm driving engagement between catches 24 and 34. The output bar 33 is accordingly driven in an upward direction, in a power stroke, as catch 24 is in turn driven upwardly.

As output bar 33 moves upwardly, it releases vertical block 74', and block 74 is in turn moved upwardly by the force of spring 77. The resultant upward movement of inclined surface 74a of block 74, releases sliding bolt 70; and said bolt is forced in a rearward direction by spring 71 to cause its leg 70c to underlie a portion of treadle bar 17a rearward of opening 17c (as illustrated in FIG. 4). This in turn locks the rear end of treadle bar 170 in its elevated position, i.e., locks the treadle mechanism in its depressed position, thereby preventing any further depression of foot pedal 17 as the power stroke continues.

it will be appreciated that the upward movement of wedge block 51 resulting from depression of pedal 17, and the pressure exerted on block 51 by pressure plate 54, causes wedge block 51 now to extend into the region previously occupied by catch 34. If this positioning of parts were to remain unchanged upon comple- "tion of the power stroke, catch 34 would be prevented 'from disengaging catch 24, i.e., power strokes would continue repetitively thereafter. Since the power assist of the present invention is intended to provide a single power stroke for each depression of the treadle mechanism, it is therefore necessary to reposition wedge block 51 prior to completion of the power stroke so as to provide aspace into which catch 34 can be moved upon completion of the power stroke, to permit disengagement between catches 34 and 24. This repositioning of wedge block 51 is effected by the tiltablelever mechanism 60.

More particularly, and recalling that lever arms 61 normally have their lower ends in a forward position at commencement of the power stroke (see PEG. 3), as the output bar 33 is driven upwardly the lug 40 attached thereto engages roller 64 on the tilt lever mechanism to force the upper end of the tilt lever mechanism in a forward direction and consequently to cause the lower ends of the lever arms 61 to move rearwardly (see FIG. 4). This rearward movement at the lower ends of the lever arms 61 causes a similar rearward movement of wedge block 51 against the force of pressure plate 54, due to the engagement between brackets 66 and pins 52 on the wedge block 51. When the lower ends of the tilt lever mechanism have been moved rearwardly in this fashion, they are held in their rearward position by engagement of spring pressed pins 70 in forward notches 68 during further progress of the power stroke.

The power stroke continues as catch 24 is driven to its uppermost position and as it is thereafter moved downwardly by the drive source. As power driven catch 24 moves downwardly, output bar is similarly moved in a downward direction by retracting springs 46, and

catches 24 and 34 remain in engagement with one another. This condition persists until catch 34 reaches opening 31a in plate 31, at which time catch 34 is moved rearwardly, by the force of leaf spring 39, into the region previously made available by the operation of the tilting lever mechanism 60. At this time, catches 34 and 24 disengage, and the power stroke is concluded with output bar 33 being maintained in its lowermost position by retracting springs 46.

When the output bar 33 has returned to its lowermost position, it reengages vertical block 74 to push it downwardly against the force of spring 77; and inclined surface 740 thereupon moves sliding bolt in a forward position against the force of its spring 71. This unlocks the treadle mechanism, and the treadle bar is pulled in an upward direction, forwardly of its pivot 1711, by springs 18. As foot pedal 17 is returned to its undepressed position, wedge block 51 is simultaneously pulled downwardly; and as its pins 52 are pulled along cam surface 66a of brackets 66, the brackets are simultaneously forced in a forward direction to reposition the tilt lever mechanism 60 to its starting position, where it is held by reengagement of spring pressed pins 70 in notches 67. This completes the single punch cycle, and the machine is now in its starting position preparatory to a next cycle, which can be initiated by again depressing the foot pedal 17.

While I have thus described a preferred embodiment of the present invention, many variations will be suggested to those skilled in the art. It must therefore be understood that the foregoing description is intended to be illustrative only, and not limitative of the present invention; and all such variations as are in accord with the principles described are meant to fall within the scope of theappended claims.

Having thus described my invention, I claim:

l. A mechanical power assist apparatus comprising an elongated output bar mounted for reciprocating motion, first resilient means biasing said bar to a predetermined quiescent position, a first catch, power driven means for continually reciprocating said first catch along a straight line path substantially parallel to the direction of extension of said output bar, a second catch movably attached to said output bar, second resilient means normally urging said second catch to a position spaced from the path of movement of said first catch, operator means for selectively moving said second catch against the restraint of said second resilient means to a position overlying said path of movement of said first catch to permit said reciprocating first catch to then engage said second catch and to move said second catch and the attached output bar away from its quiescent positionagainst the restraint of said first resilient means in a power stroke,.and means operable to-disengage said second catch from said first catch upon completion of said power stroke.

2. The apparatus of claim 1 wherein said second catch is pivotally attached to said output bar, said operator means comprising a foot-operated treadle arranged to effect pivotal movement of said second catch relative to said output bar.

3. The apparatus of claim 2 wherein said first catch comprises a bifurcated element having a roller mounted between the bifurcations thereof, said treadle including a wedge member pivotally attached thereto and positioned to engage said roller upon depression of said treadle thereby to effect said pivotal movement of said second catch.

4. The apparatus of claim 2 including locking means responsive to depression of said treadle for locking said treadle in its depressed position, and unlocking means responsive to return of said output bar to its quiescent position, upon completion of said power stroke, for unlocking said treadle.

5. The apparatus of claim 4 wherein said locking means comprises a spring biased member mounted for slidable movement to a position under a portion of said treadle, said member having an inclined surface, said unlocking means comprising a movable wedge adapted to engage said inclined surface to effect slidable movement of said member against its spring bias.

6. The apparatus of claim 1 wherein said power driven means comprises a pulley mounted for rotary motion, a motor for rotating saidpulley, said first catch being located at a position spaced from the axis of rotation of said pulley, and means responsive to rotary inotion of said pulley for effecting straight line motion of said first catch.

7. The apparatus of claim 3 including resilient means for urging said wedge member toward said roller, a movable lever mechanism mounted adjacent said wedge member, and means responsive to occurrence of said power stroke for causing said lever mechanism to move said wedge member away from said output bar against the restraint of said resilient means thereby to create a space into which said second catch can be moved upon completion of said power stroke to effect disengagement of said first and second catches.

8. The apparatus of claim 7 including reset means for returning said lever mechanism to a starting position upon completion of said power stroke.

9. The apparatus of claim 8 wherein said wedge member includes at least one outstanding pin, cam means attached to said lever mechanism adjacent said pin, and spring means urging said treadle toward its undepressed position, said treadle, when'unlocked, being moved to its undepressed position by its associated spring means thereby to effect return movement of said wedge member, said pin thereby engaging said cam means to move said lever mechanism to its starting position.

10. The apparatus of claim 9 including spring biased detent means for holding said lever mechanism in either of two predetermined positions 

1. A mechanical power assist apparatus comprising an elongated output bar mounted for reciprocating motion, first resilient means biasing said bar to a predetermined quiescent position, a first catch, power driven means for continually reciprocating said first catch along a straight line path substantially parallel to the direction of extension of said output bar, a second catch movably attached to said output bar, second resilient means normally urging said second catch to a position spaced from the path of movement of said first catch, operator means for selectively moving said second catch against the restraint of said second resilient means to a position overlying said path of movement of said first catch to permit said reciprocating first catch to then engage said second catch and to move said second catch and the attached output bar away from its quiescent position against the restraint of said first resiLient means in a power stroke, and means operable to disengage said second catch from said first catch upon completion of said power stroke.
 1. A mechanical power assist apparatus comprising an elongated output bar mounted for reciprocating motion, first resilient means biasing said bar to a predetermined quiescent position, a first catch, power driven means for continually reciprocating said first catch along a straight line path substantially parallel to the direction of extension of said output bar, a second catch movably attached to said output bar, second resilient means normally urging said second catch to a position spaced from the path of movement of said first catch, operator means for selectively moving said second catch against the restraint of said second resilient means to a position overlying said path of movement of said first catch to permit said reciprocating first catch to then engage said second catch and to move said second catch and the attached output bar away from its quiescent position against the restraint of said first resiLient means in a power stroke, and means operable to disengage said second catch from said first catch upon completion of said power stroke.
 2. The apparatus of claim 1 wherein said second catch is pivotally attached to said output bar, said operator means comprising a foot-operated treadle arranged to effect pivotal movement of said second catch relative to said output bar.
 3. The apparatus of claim 2 wherein said first catch comprises a bifurcated element having a roller mounted between the bifurcations thereof, said treadle including a wedge member pivotally attached thereto and positioned to engage said roller upon depression of said treadle thereby to effect said pivotal movement of said second catch.
 4. The apparatus of claim 2 including locking means responsive to depression of said treadle for locking said treadle in its depressed position, and unlocking means responsive to return of said output bar to its quiescent position, upon completion of said power stroke, for unlocking said treadle.
 5. The apparatus of claim 4 wherein said locking means comprises a spring biased member mounted for slidable movement to a position under a portion of said treadle, said member having an inclined surface, said unlocking means comprising a movable wedge adapted to engage said inclined surface to effect slidable movement of said member against its spring bias.
 6. The apparatus of claim 1 wherein said power driven means comprises a pulley mounted for rotary motion, a motor for rotating said pulley, said first catch being located at a position spaced from the axis of rotation of said pulley, and means responsive to rotary motion of said pulley for effecting straight line motion of said first catch.
 7. The apparatus of claim 3 including resilient means for urging said wedge member toward said roller, a movable lever mechanism mounted adjacent said wedge member, and means responsive to occurrence of said power stroke for causing said lever mechanism to move said wedge member away from said output bar against the restraint of said resilient means thereby to create a space into which said second catch can be moved upon completion of said power stroke to effect disengagement of said first and second catches.
 8. The apparatus of claim 7 including reset means for returning said lever mechanism to a starting position upon completion of said power stroke.
 9. The apparatus of claim 8 wherein said wedge member includes at least one outstanding pin, cam means attached to said lever mechanism adjacent said pin, and spring means urging said treadle toward its undepressed position, said treadle, when unlocked, being moved to its undepressed position by its associated spring means thereby to effect return movement of said wedge member, said pin thereby engaging said cam means to move said lever mechanism to its starting position. 